CMake: show Win32 and Generator_platform build-option values

Ensure key CMake option values are part of the CMake output to
facilitate user support when tool updates impact the wider CMake
actions, particularly ongoing 'improvements' in Visual Studio.

These CMake displays perform the same function as the build-options.txt
provided in the main Git for Windows. CMake is already chatty.
The setting of CMAKE_EXPORT_COMPILE_COMMANDS is also reported.

Include the environment's CMAKE_EXPORT_COMPILE_COMMANDS value which
may have been propogated to CMake's internal value.

Testing the CMAKE_EXPORT_COMPILE_COMMANDS processing can be difficult
in the Visual Studio environment, as it may be cached in many places.
The 'environment' may include the OS, the user shell, CMake's
own environment, along with the Visual Studio presets and caches.

See previous commit for arefacts that need removing for a clean test.

Signed-off-by: Philip Oakley <philipoakley@iee.email>

contrib/buildsystems/CMakeLists.txt

@@ -63,10 +63,20 @@ endif()
 
 if(NOT DEFINED CMAKE_EXPORT_COMPILE_COMMANDS)
 	set(CMAKE_EXPORT_COMPILE_COMMANDS TRUE)
+	message("settting CMAKE_EXPORT_COMPILE_COMMANDS: ${CMAKE_EXPORT_COMPILE_COMMANDS}")
 endif()
 
 if(USE_VCPKG)
 	set(VCPKG_DIR "${CMAKE_SOURCE_DIR}/compat/vcbuild/vcpkg")
+	message("WIN32: ${WIN32}") # show its underlying text values
+	message("VCPKG_DIR: ${VCPKG_DIR}")
+	message("VCPKG_ARCH: ${VCPKG_ARCH}") # maybe unset
+	message("MSVC: ${MSVC}")
+	message("CMAKE_GENERATOR: ${CMAKE_GENERATOR}")
+	message("CMAKE_CXX_COMPILER_ID: ${CMAKE_CXX_COMPILER_ID}")
+	message("CMAKE_GENERATOR_PLATFORM: ${CMAKE_GENERATOR_PLATFORM}")
+	message("CMAKE_EXPORT_COMPILE_COMMANDS: ${CMAKE_EXPORT_COMPILE_COMMANDS}")
+	message("ENV(CMAKE_EXPORT_COMPILE_COMMANDS): $ENV{CMAKE_EXPORT_COMPILE_COMMANDS}")
 	if(NOT EXISTS ${VCPKG_DIR})
 		message("Initializing vcpkg and building the Git's dependencies (this will take a while...)")
 		execute_process(COMMAND ${CMAKE_SOURCE_DIR}/compat/vcbuild/vcpkg_install.bat ${VCPKG_ARCH})